Flexible bone screw

ABSTRACT

A flexible bone screw for insertion into the intramedullary cavity of a fractured bone facilitates enduring fixation of the fracture. The flexible bone screw includes a substantially smooth shaft and a threaded portion positioned at one end of the shaft, wherein the outer diameter of the threaded portion is greater than the shaft diameter and the length of the threaded portion is about 20% of the overall length of the flexible bone screw or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/462,494, filed on Aug. 18, 2014, entitled “FLEXIBLE BONE SCREW”,which is a divisional of U.S. patent application Ser. No. 11/951,282,filed on Dec. 5, 2007, entitled “FLEXIBLE BONE SCREW”, now U.S. Pat. No.8,808,338, issued Aug. 19, 2014, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate generally to orthopedicsurgery and, more particularly, to bone screws for management of bonefractures.

Description of the Related Art

Surgical techniques for the treatment of bone fractures commonly knownand used in the art include external fixation, pinning, and jointreplacement. In some situations, each of these techniques can beinadequate for facilitating satisfactory recover of the bone fracture.

A proximal humerus fracture, i.e., a fracture of the humerus near thehumeral head, is one such case. Replacement of the shoulder joint with aprosthesis is a complex and invasive procedure that can lead to thedeath of elderly patients, for whom proximal humerus fractures arecommon. External fixation of a proximal humerus fracture with one ormore humeral plates and bone screws may successfully maintain thecorrect position of the humerus fragments, but the extensive dissectionof soft tissue that is an integral part of this approach leads to highmorbidity.

As illustrated in FIG. 1A, rigid, threaded-tip pins 101 may be used forpercutaneous fixation of a humeral head 102 of a humerus 100 to boneshaft 103 to treat a proximal humerus fracture 120. Threaded-tip pins101 are inserted through cortex 105 and into subchondral bone 106 ofhumeral head 102. In elderly patients who have suffered a proximalhumerus fracture, bone of humeral head 102 is generally porous and softand tends to collapse subsequent to fracture reduction and pinning. Thecollapse tends to occur adjacent to fracture 120, where the bone is alsomost fragmented. Further, the soft bone of humeral head 102 does nothold the tips of threaded-tip pins 101 securely. Because threaded-tippins 101 are held in place at a single point that is relatively far fromsubchondral bone 106, i.e., penetration point 104 of cortex 105,threaded-tip pins 101 are free to angulate or tilt about penetrationpoint 104 and therefore offer little stability to humeral head 102.Collapse or fragmentation of the bone of humeral head 102 and poorfixation of threaded-tip pins 101 in subchondral bone 106 allow furthermovement between humeral head 102 and bone shaft 103. A displacementforce is applied by muscles to bone shaft 103, further causing movementat fracture 120. Tilting of threaded-tip pins 101 allows humeral head102 to be angulated and displaced from bone shaft 103, as illustrated inFIG. 1B. Such angulation and displacement require additional surgery forsatisfactory recovery of proximal humerus fracture 120.

FIG. 2A illustrates another prior art method for percutaneous fixationof the humeral head 202 of a humerus 200 to a bone shaft 203 to treat aproximal humerus fracture 230. First, humeral head 202 is returned toits proper position on bone shaft 203, using methods standard to the artof orthopedic surgery. Then, one or more fully-threaded K-wires 201 areintroduced into the intramedullary cavity 210 of humerus 200 through anopening 204 in the antero-lateral cortex 205 of humerus 200. Forclarity, only one fully-threaded K-wire 201 is depicted in FIG. 2A.Fully-threaded K-wires 201 are then advanced into the intramedullarycavity 210, along far cortex 207, and threaded into the subchondral bone206. Because each fully threaded K-wire 201 is supported by far cortex207 and is not free to angulate or tilt, humeral head 202 is not subjectto angulation or displacement if subchondral bone 206 collapses afterfixation or if fixation of K-wire 201 in humeral head 202 is suboptimal.However, collapse of humeral head 202 does produce other complicationswhen the method illustrated in FIG. 2A is used to fixate proximalhumeral fracture 230.

FIG. 2B illustrates humerus 200 after fixation with one or morefully-threaded K-wires 201. As shown, collapse of bone adjacent tofracture 230 results in penetration of the shoulder joint by fullythreaded k-wire 201. This is because the threads on the shaft of fullythreaded K-wire 201 engage the edges of opening 204 and hold fullythreaded K-wire 201 in place as bone adjacent to fracture 230 collapses.Even if opening 204 is over-sized relative to the outer diameter offully threaded K-wire 201, the threads on the shaft of fully threadedK-wire 201 engage the edge of opening 204 due to loading caused by theelastic bend in fully threaded K-wire 201. In addition, fully threadedK-wire 201 has limited holding power in the relatively soft material ofsubchondral bone 206, since fully threaded K-wire 201 must have arelatively small diameter in order to have the necessary flexibility forinsertion into humerus 200. The limited holding power of fully threadedK-wire 201 further encourages penetration of the joint as bone adjacentto fracture 230 collapses. Joint penetration by fully threaded K-wire201 can lead to unwanted cartilage and bone damage and requiresimmobilization of the joint for the duration of treatment, i.e., untilproximal humeral fracture 230 has healed and fully threaded K-wire 201has been removed.

An additional complication associated with the approach illustrated inFIG. 2A is K-wire breakage. Some small diameter models of fully threadedK-wires known in the art have sufficient flexibility for use as fullythreaded K-wire 201 as described above. However, it is known that thebending moment exerted on fully threaded K-wire 201 when rotationallyinserted into humerus 200 can result in breakage of fully threadedK-wire 201 in the intramedullary cavity 210, which is highlyundesirable. This breakage is related to the notch effect of the threadson the shaft of K-wire 201. Rotation of the elastically bent K-wire 201during insertion causes cyclic loading that accentuates the notcheffect.

A further complication of K-wire usage is the penetration of far cortex207. If the tips are too sharp, i.e., the included angle of the point istoo small, K-wire 201 tends to penetrate far cortex 207 rather thanslide or rotationally advance along the inner surface of far cortex 207as it is rotationally inserted. This problem is especially notable fortrocar point K-wires. A further reason for penetration of far cortex 207is that there is lacking instrumentation and methodology which candirect the K-wires away from entry into far cortex 207.

Accordingly, there is a need in the art for devices and methods for themanagement of bone fractures which prevent angulation and displacementof bone fragments, do not result in joint penetration by repair devicesdue to collapse of bone of the head, avoid breakage of repair devicesinside the fractured bone, and avoid penetration of the far cortex byrepair devices during their insertion.

SUMMARY OF THE INVENTION

The present invention provides devices and methods used in repairingbone fractures. According to one embodiment of the invention, a flexiblebone screw comprises a shaft and a threaded portion at one end of theshaft, where the threaded portion has an outer diameter that is largerthan the shaft diameter and a length that is 20% of the length of theflexible bone screw or less, and the ratio of the length of the flexiblebone screw to the shaft diameter is at least 50.

According to another embodiment of the invention, a flexible bone screwcomprises a first end including a tool engagement portion, a second endincluding a threaded portion, and a shaft between the first end and thesecond end. In this embodiment, the tool engagement portion has adiameter that is substantially the same or less than the shaft diameter,which is 3 mm or less, and the threaded portion has an outer diameterthat is larger than the shaft diameter and a length that is 20% of thelength of the flexible bone screw or less.

According to another embodiment of the invention, a method for repairinga bone fracture comprises the steps of inserting a flexible bone screwretrograde into a curved screw guide, inserting the curved screw guidehaving the flexible bone screw resting therein into an intramedullarycavity of the bone, rotating the flexible bone screw to connect theflexible bone screw to a portion of the bone, and removing the curvedscrew guide from the intramedullary cavity after connecting the flexiblebone screw to the portion of the bone.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A and 1B illustrate threaded-tip pins used for percutaneousfixation of a humeral head of a humerus to bone shaft to treat aproximal humerus fracture.

FIGS. 2A and 2B illustrate percutaneous fixation of the humeral headwith one or more fully-threaded K-wires to treat a proximal humerusfracture.

FIG. 3 depicts a flexible bone screw configured for percutaneousmanagement of proximal humerus fractures, according to one embodiment ofthe invention.

FIGS. 4A and 4B illustrate a flexible bone screw inserted obliquely intoan antero-lateral opening in a cortex of a humerus.

FIG. 5 illustrates the elastic bending arc of a flexible bone screw.

FIG. 6 illustrates a partial schematic view of a flexible bone screwhaving a tapered portion joining a shaft and a threaded portion,according to one embodiment of the invention.

FIG. 7 illustrates a partial cross-sectional view of a flexible bonescrew having a threaded portion, where the tip of the threaded portionhas an included angle that is at least 80°, according to an embodimentof the invention.

FIGS. 8A-H illustrate drill tips that may be incorporated into aflexible bone screw, according to embodiments of the invention.

FIG. 9 illustrates a cross-sectional view of a threaded portion of aflexible bone screw, according to embodiments of the invention.

FIGS. 10A-F illustrate tool engagement portions that may be incorporatedinto a flexible bone screw, according to embodiments of the invention.

FIG. 11 schematically illustrates a curved screw guide, according to anembodiment of the invention.

FIGS. 12A and 12B illustrate a curved screw guide with a flexible bonescrew positioned therein.

FIG. 13 is a flow chart summarizing a sequence of steps for repairing abone fracture using a flexible bone screw and curved screw guide,according to an embodiment of the invention.

FIG. 14 illustrates the insertion of a guide wire into the cortex of ahumerus, according to an embodiment of the invention.

FIG. 15 illustrates a cannulated drill bit positioned around a guidewire immediately prior to drilling an opening into a cortex of ahumerus, according to an embodiment of the invention.

For clarity, identical reference numbers have been used, whereapplicable, to designate identical elements that are common betweenfigures. It is contemplated that features of one embodiment may beincorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments of the invention contemplate a flexible bone screw forinsertion into the intramedullary cavity of a fractured bone tofacilitate reduction and/or fixation of the fracture. Embodimentsfurther provide a method of flexible bone screw insertion into theintramedullary cavity of a fractured bone. The flexible bone screwaccording to embodiments of the invention prevents angulation anddisplacement between bone fragments, reduces the risk of bone screwbreakage, avoids joint penetration by the bone screw, and avoidspenetration of the bony cortex opposite the entry hole.

FIG. 3 depicts a flexible bone screw 300 configured for management ofproximal humerus fractures, e.g., percutaneous management of proximalhumerus fractures, according to one embodiment of the invention.Flexible bone screw 300 is fabricated from stainless steel and includesa shaft 301 with a shaft diameter 302 and a threaded portion 303. Thesurface of shaft 301 is substantially smooth, having a surfaceroughness, Ra, of less than about 3 micrometers, where the surfaceroughness is measured parallel to the axis of shaft 301. The smoothshaft surface allows easy gliding of shaft 301 into the entry hole, sothat if the head should collapse, shaft 301 slides out of the entry holerather than being engaged with the entry hole, which would forcethreaded portion 303 through subchondral bone with prior art devices.Threaded portion 303 is positioned at one end of shaft 301 forengagement with bone material, has a length 305, and has an outerdiameter 304 that is larger than shaft diameter 302. A tool engagementportion 307 is positioned at the opposite end of shaft 301 to facilitateattachment of flexible bone screw 300 to a manual or poweredscrew-rotating device (e.g., element 420 in FIG. 4A) and does not engageagainst bone. Flexible bone screw is configured so that tool engagementportion 307 and any extra length of shaft 301 can be cut off at thecompletion of surgery. In this embodiment, shaft diameter 302 is between1.7 mm and 3 mm; overall length 306 is at least 200 mm, preferably 300mm; length 305 is between 6 mm and 25 mm, and outer diameter 304 isbetween 3 mm and 5 mm. Having a shaft diameter less than 3 mm allows ashaft stiffness which is not excessive for manipulation by the surgeonduring surgery. In order for flexible bone screw 300 to have thenecessary flexibility as contemplated by the inventor, i.e., an elasticbending arc of at least 15°, the ratio of length 306 to shaft diameter302 is at least about 50:1. It is preferred that the elastic bending arcbe at least 30° and the ratio of length 306 to shaft diameter 302 be atleast about 100:1. This avoids use of the screw substantially in theplastic bending range to an extent that would cause mechanical failureof the screw. The elastic bending arc of a flexible bone screw isdescribed below in conjunction with FIG. 5. Tool engagement portion 307has a length that is less than one-tenth of length 306.

Other embodiments are contemplated, where one or more features offlexible bone screw 300, as described above, may have differentdimensions based on what bone is being treated, the location of thefracture, and other factors. For example, the ratio of length 305 tooverall length 306 may be as high as 0.20, the ratio of outer diameter304 to shaft diameter 302 may vary between about 1.2 and about 4.0, andthe possible elastic bending arc may be greater than 15°. Other featuresthat may have different values include shaft diameter 302, outerdiameter 304, length 305, and overall length 306. In addition, thematerial may be a titanium-based alloy, such as Ti 6-4, which wouldallow the use of higher possible shaft diameter while maintaining theflexibility to attain an elastic bending arc of 15° or greater.

In operation, as illustrated in FIG. 4A, flexible bone screw 300 isinserted obliquely into an antero-lateral opening 404 in a cortex 405 ofa humerus 400. In this embodiment, a powered screw-rotating device 420is coupled to the tool engagement portion of flexible bone screw 300 torotate flexible bone screw 300 as the screw is inserted into theintramedullary cavity 410 of humerus 400. Because flexible bone screw300 contacts far cortex 407 at an oblique angle, e.g., less than about40°, and because flexible bone screw 300 is configured to be flexibleenough to attain a substantially elastic bending arc of greater than 15°and the tip has an included angle of greater than 80°, the tip ofthreaded portion 303 does not penetrate far cortex 407 and instead isdeflected off inner surface 412 of far cortex 407.

Referring to FIG. 4B, flexible bone screw 300 is further advanced intointramedullary cavity 410 after deflecting off inner surface 412 of farcortex 407 until threaded portion 303 is engaged with subchondral bone406. In this way, flexible bone screw 300 is positioned in adistal-to-proximal (“retrograde” in orthopedic parlance) orientation,i.e., substantially parallel to the major axis of humerus 400, so thathumeral head 402 is not subject to angulation and displacement afterfixation of proximal humerus fracture 430 if bone adjacent to fracture430 collapses. In the event of bone collapse, flexible bone screw 300 isfree to slide back out of antero-lateral opening 404, since shaft 301 offlexible bone screw 300 is substantially smooth, thereby preventingjoint penetration by flexible bone screw 300. In addition, because outerdiameter 304 of threaded portion 303 is larger than shaft diameter 302,flexible bone screw 300 has more holding power in subchondral bone 406than the holding power of the fully threaded K-wire used in the priorart, which has an outer diameter equal to shaft diameter 302. Theimproved holding power of threaded portion 303 secures proximal humerusfracture 430 in place and suppresses joint penetration by flexible bonescrew 300 due to bone collapse. Additionally, the shaft 301 is lesssusceptible to breakage during advancement since it is substantiallysmooth and does not include threads. The smooth surface of shaft 301also facilitates removal from humerus 400.

FIG. 5 illustrates the elastic bending arc 501 of a flexible bone screw502, where flexible bone screw 502 represents flexible bone screw 300described in FIG. 3. Elastic bending arc 501 is defined as the maximumarc of curvature, in degrees, that can be produced by flexible bonescrew 502 without flexible bone screw 502 undergoing substantial plasticdeformation. Hence, a more flexible bone screw has an elastic bendingarc of greater degree than a less flexible bone screw. The elasticbending arc of the flexible bone screws according to the embodiments ofthe invention is by design much greater than any other prior art bonescrews made of the same metal, and this characteristic addressesspecific previously unsolved needs in fracture treatment, and thischaracteristic has been achieved by carefully adjusting the dimensionsin a way that is not observed in the prior art. The achievement of thespecial dimensions requires special and difficult manufacturingtechniques not previously seen in the field of the invention, techniqueswhich would not be developed if the dimensions did not offer unique,novel advantages, as has been demonstrated by the inventor.

One reason for the importance of the ratio of the length 306 to shaftdiameter 302 and bending arc 501 is that they largely define how easilythe bone screw may be manipulated by the surgeon. The surgeon must beable to bend the bone screw to a minimum arc of 15°, and preferably toan arc of 30°, without the use of excessive force or localized glovepressure, in order to insert the bone screw with hand held tools. Forlarger shaft diameters, the surgeon obtains greater bending leverage byhaving a correspondingly longer bone screw length 306, but the elasticbending arc, in such a case, would remain the same. The inventor hasdetermined that, for the humerus bone and stainless steel screws,preserving manipulability by preserving elastic bending arc is valid upto shaft diameter 302 of about 3 mm. Other metal alloys with lowerelastic modulus allow slightly greater shaft diameter 302.

FIG. 6 illustrates a partial schematic view of a flexible bone screw 600having a tapered portion 608 joining a shaft 601 and a threaded portion603, according to one embodiment of the invention. In this embodiment,threaded portion 603 has an inner diameter 609 that is larger than shaftdiameter 602. The inventor has determined that when inner diameter 609of threaded portion 603 is larger than shaft diameter 602, breakage inthe location where shaft 601 joins threaded portion 603 is avoided.

FIG. 7 illustrates a partial cross-sectional view of a flexible bonescrew 700 having a threaded portion 703, where the tip 710 of threadedportion 703 has an included angle 711 that is at least 80°, according toan embodiment of the invention. In this embodiment, tip 710 of flexiblebone screw 700 is optimized to improve the performance of flexible bonescrew 700 when flexible bone screw 700 first contacts an internalsurface of the humerus cortex. To minimize the potential for penetrationof the far cortex of a bone, for example far cortex 407 of humerus 400,illustrated in FIGS. 4A and 4B, the tip of threaded portion 703 offlexible bone screw 700 is designed to have an included angle of atleast 80°. The inventor has determined that when tip 710 contacts asurface at a non-normal angle and included angle 711 is substantiallyless than 80°, tip 710 may still penetrate the surface, rather thanbeing deflected. Hence, as flexible bone screw 700 is inserted obliquelyinto the intramedullary cavity of a fractured bone and included angle711 is at least about 80°, flexible bone screw 700 glances off the innersurface of the far cortex.

The inventor has also determined that the tip configuration of aflexible bone screw may be optimized to improve the penetration andholding power of the bone screw when the bone screw engages subchondralbone material. In different situations, it is contemplated that a spadetip, trocar tip, threaded tip, or a corkscrew tip may be beneficiallyincorporated into a flexible bone screw for improved performance.

FIG. 8A illustrates a side view of a spade tip 810 that may beincorporated into a flexible bone screw, according to an embodiment ofthe invention. FIG. 8B illustrates a 90-degree rotated view of spade tip810. FIG. 8C illustrates a partial side view of a trocar tip 820 thatmay be incorporated into a flexible bone screw, according to anembodiment of the invention. FIG. 8D illustrates a head-on view oftrocar tip 820. FIG. 8E illustrates a side view of a threaded tip 830that may be incorporated into a flexible bone screw, according to anembodiment of the invention. In the embodiment depicted in FIG. 8E,threaded tip screw 830 is a double lead threaded screw tip; however,other varieties of threaded tips are also contemplated as part of aflexible bone screw. FIG. 8F illustrates a partial side view of acorkscrew tip 840 that may be incorporated into a flexible bone screw,according to an embodiment of the invention. As shown, corkscrew tip 840has a tapered core tip, where the core may end before the tip of thescrew. FIG. 8G illustrates a side view of a fluted screw tip 850 havingforward cutting flutes 851 and a reverse cutting flute 852. FIG. 8Hillustrates a head-on view of fluted screw tip 850. Forward cuttingflutes 851 and reverse cutting flute 852 facilitate the penetration offluted screw tip 850 into subchondral or other bone material during bonefragment fixation, and the reverse cutting flutes facilitate subsequentremoval after fracture healing. In addition, the penetration efficiencyof a flexible bone screw may be enhanced by configuring the outerdiameter of the threaded portion of the bone screw to be smaller at thetip of the threaded portion, according to one embodiment of theinvention. Examples of this embodiment are illustrated in FIGS. 8E and8F.

The inventor has also determined that the thread configuration of thethreaded portion of a flexible bone screw may be optimized to improvethe holding power of the bone screw in subchondral or other relativelysoft bone material by maximizing the surface area of each thread incontact with surrounding bone tissue and minimizing displacement of bonevolume. It is contemplated that a number of factors related to threadconfiguration may be so optimized, including thread width relative tothread diameter, and the ratio of thread pitch to thread outer diameter.FIG. 9 illustrates a cross-sectional view of a threaded portion 900 of aflexible bone screw, according to embodiments of the invention. Threadpitch diameter is defined as the sum of thread outer diameter 905 pluscore diameter 907, divided by two. Holding power of threaded portion 900is improved when thread width 901 of threads 902 at thread pitchdiameter 903 is less than one half of thread pitch 904. Holding power ofthreaded portion 900 is also improved when the ratio of thread pitch 904to outer thread diameter 905 is greater than about 0.2 and less thanabout 0.5.

It is contemplated that the tool engagement portion of a flexible bonescrew may have various configurations, including straight-ended,rounded, threaded, a hex recess with increased diameter, reduceddiameter, and flat-sided. FIG. 10A illustrates an end-on view and apartial side view of a straight-ended tool engagement portion 1001 thatmay be incorporated into a flexible bone screw, according to anembodiment of the invention. FIG. 10B illustrates an end-on view and apartial side view of a rounded tool engagement portion 1002 that may beincorporated into a flexible bone screw, according to an embodiment ofthe invention. Rounded tool engagement portion 1002 serves to preventpuncture of a surgeon's glove during surgery, and to aid in retrogradeinsertion of a flexible bone screw into a curved screw guide, which isdescribed below in conjunction with FIG. 11. FIG. 100 illustrates anend-on view and a partial side view of a threaded tool engagementportion 1003 that may be incorporated into a flexible bone screw,according to an embodiment of the invention. The threaded portion ofthreaded tool engagement portion 1003 engages in an internally threadedportion of a standard surgical insertion tool. FIG. 10D illustrates anend-on view and a partial side view of a tool engagement portion 1004having a hex recess that may be incorporated into a flexible bone screw,according to an embodiment of the invention. FIG. 10E illustrates anend-on view and a partial side view of a tool engagement portion 1005having a reduced diameter that may be incorporated into a flexible bonescrew, serving to engage a standard K-wire driving tool (e.g., tool 420shown in FIG. 4A) which will not accommodate the full diameter of theshaft, according to an embodiment of the invention. FIG. 10F illustratesan end-on view and a partial side view of a tool engagement portion 1006with multiple flat sides that may be incorporated into a flexible bonescrew, according to an embodiment of the invention for accommodationwithin the jaws of a standard surgical drill chuck.

Embodiments of the invention further contemplate a curved screw guideconfigured to facilitate the insertion of a flexible bone screw asdescribed herein, such as flexible bone screw 300, into theintramedullary cavity of a fractured bone. FIG. 11 schematicallyillustrates a curved screw guide 1100, according to an embodiment of theinvention. Curved screw guide 1100 may be constructed of stainless steelor other durable surgical-grade material, such as titanium andtitanium-containing alloys. Curved screw guide 1100 includes a curvedtube 1101 and a holding means 1102, such as a T-handle or other grip.Inner diameter 1103 of curved tube 1101 is selected so that the shaft ofa flexible bone screw as described herein may be inserted into curvedtube 1101 in a retrograde manner, i.e., inserted in the oppositedirection that curved tube 1101 is inserted into the intramedullarycavity. Inner diameter 1103 is selected to be smaller than the outerdiameter of the threaded portion of the flexible bone screw, so that thethreaded portion remains outside curved tube 1101 without sliding intocurved tube 1101 in the retrograde direction, and outer diameter 1104 isselected to be smaller than the outer diameter of the threaded portionof the flexible bone screw, so that entry into the bone hole is nothindered by the curved screw guide 1100. In one embodiment, innerdiameter 1103 is approximately 10% to 100% larger than the shaftdiameter of a flexible bone screw inserted therein. Curved screw guide1100 is configured so that a flexible bone screw may be guided into theintramedullary cavity of a fractured bone, and oriented appropriately toengage the humeral head or other desired bone fragment when the bonescrew is advanced into the fractured bone. Curved screw guide 1100 isalso configured to minimize the risk of the flexible bone screwpenetrating the far cortex of the fractured bone by providing a meansfor directing the flexible bone screw as required within theintramedullary cavity. The minimum radius of curvature of curved screwguide 1100 varies depending on the shaft diameter and the material ofthe flexible bone screw being inserted. In one embodiment of a stainlesssteel screw, the minimum radius of curvature of the curved screw guide1100 is no less than 90 times the shaft diameter of the flexible bonescrew. The inventor has determined that the approximate minimum radiusof curvature for stainless steel is 90*d where d is the shaft diameter.Alloys with higher elastic limit, such as titanium alloys, allow aradius of curvature less than 90*d. Thus, if the minimum radius ofcurvature of the curved screw guide 1100 is no less than 90 times theshaft diameter of the flexible bone screw, substantial plasticdeformation of the flexible bone screw inserted into the curved screwguide 1100 is avoided. It is understood that the curved screw guide 1100can be constructed to have a portion which is tangent to a portion whichis curved and that the radii of curvature of the curved screw guide 1100can vary at different positions along the length thereof.

FIG. 12A illustrates a curved screw guide 1201 with a flexible bonescrew 1202 positioned therein after insertion into the intramedullarycavity 1210 of a humerus 1205 and prior to advancement of flexible bonescrew 1202 across a fracture 1203 and into the humeral head 1204. Asshown, threaded portion 1206 is not contained in curved tube 1207 ofcurved screw guide 1201, and is oriented toward humeral head 1204 withreduced contact against far cortex 1208. FIG. 12B illustrates curvedscrew guide 1201 with flexible bone screw 1202 therein, after engagementof threaded portion 1206 with the subchondral bone 1209 of humeral head1204.

FIG. 13 is a flow chart summarizing a sequence of steps 1300 forrepairing a bone fracture using a flexible bone screw and curved screwguide, according to an embodiment of the invention. In this embodiment,a proximal humerus fracture is repaired, although it is contemplatedthat other fractures may be treated in a similar manner.

In step 1301, an opening is formed in the cortex of a humerus bone at anoblique angle to expose the intramedullary cavity of the bone. Theopening may be formed in a conventional manner, i.e., by drilling intothe cortex at an oblique angle. Alternatively, a pointed guide wire mayfirst be inserted into the cortex to guide the larger drill into thebone without slipping off the bone. FIG. 14 illustrates the insertion ofa guide wire 1401 into the cortex 1402 of a humerus 1403, according toan embodiment of the invention. The opening is then formed in the cortexof the humerus using a cannulated drill bit that is positioned aroundthe guide wire. In this way, the drill angle of entry into the cortexcan be set without slippage off the bone and secondary injury toadjacent bone structures, thereby better facilitating the step ofinserting the curved screw guide into the intramedullary cavity. FIG. 15illustrates a cannulated drill bit 1501 positioned around guide wire1401 immediately prior to drilling an opening into cortex 1402 ofhumerus 1403.

In step 1302, a flexible bone screw is inserted retrograde into a curvedscrew guide, where the flexible bone screw is substantially similar inorganization and operation to flexible bone screw 300 in FIG. 3. Becauseof the retrograde insertion of the flexible bone screw into the curvedscrew guide, the shaft of the bone screw is contained in the curvedscrew guide and the threaded portion of the bone screw is positionedoutside the curved screw guide at the insertion end thereof.

In step 1303, the curved screw guide and flexible bone screw areinserted into the intramedullary cavity of the fractured bone via theopening in the cortex. In step 1304, the flexible bone screw is orientedas desired by positioning the curved screw guide in the intramedullarycavity of the fractured bone. In step 1305, the flexible bone screw isrotated and advanced into the intramedullary cavity until the threadedportion of the flexible bone screw engages the subchondral bone of thehumeral head. In step 1306, the curved screw guide is removed from theintramedullary cavity. The extra length of the screw shaft projectingfrom the bone and the surgical wound are then cut off, leaving enough tofacilitate removal, according to standard surgical techniques. It iscontemplated by the inventor that in certain cases, the dimensions andhardness of the bone and flexibility of the screw may allow insertion ofthe flexible bone screw without the aid of the curved screw guide.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for repairing a bone fracture,comprising the steps of: drilling a hole through a side of the bone toexpose an intramedullary cavity of the bone; inserting a flexible bonescrew through the hole into the intramedullary cavity of the bone, theflexible bone screw having an elongated shaft and a threaded portion ata leading end thereof; and rotating the bone screw to advance thethreaded portion of the bone screw with associated elastic bending ofthe shaft, substantially along a longitudinal axis of the bone; andinserting the tip of the threaded portion past the location of the bonefracture.
 2. The method according to claim 1, wherein the side of thebone comprises a cortex of the bone.
 3. The method according to claim 1,wherein the drilled hole is an oblique hole.
 4. The method according toclaim 1, wherein, with the associated elastic bending of the screw, thethreaded portion is advanced within the intramedullary cavity of thebone in a direction that is approximately parallel to the longitudinalaxis of the bone.
 5. The method according to claim 1, wherein, with theassociated elastic bending of the screw, the threaded portion isadvanced within the intramedullary cavity of the bone along a firstdirection that is substantially different from a second direction alongwhich the threaded portion was inserted into the intramedullary cavityof the bone.
 6. The method according to claim 5, wherein the firstdirection is more parallel to the longitudinal axis of the bone than thesecond direction.
 7. The method according to claim 1, wherein a ratio ofthe length of the threaded portion to the length of the flexible bonescrew is less than 0.2 or less.
 8. The method according to claim 7,wherein a ratio of the length of the flexible bone screw to the diameterof the shaft is at least 50, and a material for the flexible bone screwis one of stainless steel, titanium, or titanium alloy.
 9. The methodaccording to claim 7, wherein an elastic bending arc that is attainableby the flexible bone screw is at least 15 degrees.
 10. A method forrepairing a bone fracture, comprising the steps of: drilling a holethrough a side of the bone to expose an intramedullary cavity of thebone; inserting a flexible bone screw through the hole in a firstdirection, into the intramedullary cavity of the bone, the flexible bonescrew having an elongated shaft and a threaded portion at a leading endthereof; and rotating the bone screw to advance the threaded portion ofthe bone screw with associated elastic bending of the shaft, in adirection that is along a longitudinal axis of the bone; and insertingthe tip of the threaded portion past the location of the bone fracture.11. The method according to claim 10, wherein the side of the bonecomprises a cortex of the bone.
 12. The method according to claim 10,wherein the drilled hole is an oblique hole.
 13. The method according toclaim 10, wherein the first direction forms an oblique angle withrespect to a longitudinal axis of the bone.
 14. The method according toclaim 10, wherein the second direction is approximately parallel to alongitudinal axis of the bone.
 15. The method according to claim 10,wherein a ratio of the length of the threaded portion to the length ofthe flexible bone screw is less than 0.2 or less.
 16. The methodaccording to claim 15, wherein a ratio of the length of the flexiblebone screw to the diameter of the shaft is at least 50, and a materialfor the flexible bone screw is one of stainless steel, titanium, ortitanium alloy.
 17. The method according to claim 15, wherein an elasticbending arc that is attainable by the flexible bone screw is at least 15degrees.
 18. The method according to claim 15, wherein an elasticbending arc that is attainable by the flexible bone screw is at least 30degrees.
 19. A method for repairing a fracture of a humeral head,comprising the steps of: drilling a hole through a side of a humerusbone to expose an intramedullary cavity of the humerus bone; inserting aflexible bone screw through the side of the humerus bone into theintramedullary cavity of the humerus bone, the flexible bone screwhaving an elongated shaft and a threaded portion at a leading endthereof; and rotating the bone screw to advance the threaded portion ofthe bone screw with associated elastic bending of the shaft, along adirection towards the humeral head; and inserting the tip of thethreaded portion past the location of the fracture.
 20. The methodaccording to claim 19, wherein an elastic bending arc that is attainableby the flexible bone screw is at least 15 degrees.